The storage capacity of hard drives is continuously increasing due to advancements in the accuracy and sensitivity of the magnetic read-write head assemblies incorporated into these hard drives. Due to the ever increasing levels of accuracy and sensitivity, the read-write head assemblies are increasingly difficult to manufacture, resulting in a large portion of the read-write head assemblies being tested prior to being installed in hard disk drives.
When testing a read-write head assembly, it is typically placed onto a testing system, commonly referred to as a spinstand. The spinstand typically incorporates a slide brake assembly that duplicates the movement of the read-write head assembly as if it were installed in a hard disk drive. This slide brake assembly, which is typically positionable at a low level of resolution, includes a micropositioning stand that is typically positionable at a high level of resolution.
The data tracks in a hard disk drive are concentric tracks on the surfaces of the platters of the hard disk drive, and the density of these tracks is continuously increasing (i.e., currently hard disk drives have track densities as high as 50,000–100,000 tracks per inch (tpi)).
As these densities continue to increase, the positional resolution of the slide brake assembly must increase accordingly. For example, for a hard disk drive having a density of 50,000 tpi, in order to adequately test a read-write head assembly for use in such a hard disk drive, the positional resolution of the slide brake assembly (and, therefore, the read-write head assembly) should typically be 1/100th of the track width. Accordingly, the combination of the slide brake assembly and the micropositioning stand should have a positional resolution of 0.0000002 inches. This high level of positional resolution is typically achieved through the use of a micropositioning stand that includes a piezoelectric crystal that expands and contracts based on the voltage signal applied to the crystal. Accordingly, during typical testing, the slide brake assembly is used to generally position the read-write head assembly and then the micropositioning stand accurately locates the read-write head assembly above or below the appropriate hard disk drive track.
During a typical testing sequence, the read-write head assembly to be tested is mounted to the micropositioning stand . A spindle-mounted magnetic disk is then spun at the operating speed of the target hard drive (i.e., typically between 5,400 and 20,000 rpm). The slide brake assembly generally positions the read-write head assembly proximate the test position of the rotating magnetic disk and the micropositioning stand then accurately positions the read-write head assembly. Once accurately positioned, the read-write head assembly is commanded through a series of data read-write operations to verify accuracy and sensitivity of the read-write head assembly.
As would be expected, in addition to being able to accurately position the read-write head assembly, the rate at which the read-write head assembly is repositioned must also be quite high. For example, it is desirable to be able to move the read-write head assembly from a first test position to a second test position within one disk revolution. For a disk rotating at 20,000 rpm, that is equal to three milliseconds.
In order to facilitate such quick repositioning, current spinstand designs typically include slide brake assemblies that are coarsely positioned using rail assemblies and air bearings, finely positioned using piezoelectric crystals, and clamped down to a granite surface using vacuum-evacuated platens. Unfortunately, the use of multiple air bearings often reduce overall accuracy and complicates the manufacturing process.